The Controlled Substances Act (CSA) was justified under the Interstate Commerce Clause of the U.S. Constitution. The reasoning is that the sale of narcotics crosses state lines, is part of interstate commerce, and is therefore fair game for the feds to regulate. The Ninth Circuit noted that in Raich, the cannabis in question was locally grown and sold. There was simply no connection to interstate commerce, and therefore the CSA could not apply.

Personally, I think the federal government has very little business regulating state criminal law, and the dubious connections the feds draw between essentially state matters and interstate commerce in an effort to justify federal interference reduces the legitimacy of the federal government as a whole.

It will be interesting to see how staunch states' rights advocates like Scalia and Rehnquist match up with the more traditional liberals on the court like Ginsburg and Stevens, who traditionally favor individual rights over states' rights. In this case, it seems that the two are one in the same.